Cross-field furnace having auxiliary poles without coils



L. DREYFUS A ril 29, 1958 CROSS-FIELD FURNACE HAVING AUXILIARYPOLESWITHOUT COILS Filed Sept. 11, 1956 INVENTOR. Lucia/{g Prey/ 5flffarm 6 United States Patent 1 2,832,877 CROSS-FIELD FURNACE HAVINGAUXILIARY POLES WITHOUT COILS Ludwig Dreyfus, Vasteras, Sweden, assignorto Allmiinna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a

corporation of Sweden Application September 11, 1956, Serial No. 699,169

4 Claims. (Cl. 219-44167) To the same extent as the induction heating isgaining ground in the manufacturing industry the demand for productioncapacity and automatic feed is growing.

If the inductive heating of billets is concerned good results have beenattained with a conveyer chain according to Letters Patent 2,667,524 butthis chain requires a crossfield furnace in which the main direction ofthe field is vertical when the longitudinal axis of the billet ishorizontal, and as shown in Fig. 2a of the mentioned Letters Patent, inthe known cross-field furnace the heat from the eddy currents in abillet of rectangular crosssection is produced substantially only alongthe vertical side surfaces of the billet. The equalization of thedifferenccs of the temperature across the width of the billet is left tothe conduction of heat and will be performed in minor billets where thetime constant T is only some seconds. However, the time constantincreases quadratically with the width 5 of the billet. Assuming forexample that:

Width of the billet 6 15 cm.

watt sec.

Specific heat 0=5-6 Heat transmission coefficient )\=0.3 The timeconstant will be Obviously it is impossible in practice to wait such along time for the equalization of the temperature, since the heat lossesand the oxidation of the billets would become excessive. a

According to the present invention, a substantially uni form heatingalong the periphery of the billet is attained in connection with the useof the convcyer chain mentioned above.

The particular feature of the invention is, that in a cross-fieldfurnace in which an alternating field is produced plane-parallelly andat right angles to the longitudinal axis of the billet and symmetricallythereto, and which field is completed through the billet and laminatediron yokes, there are extended from these yokes four distinct poles, ofwhich two co-axial poles having different polarities and working as mainpoles are provided with windings, while two other auxiliary polesarranged at an angle of 90 with respect to the main poles have nowindings, said auxiliary poles causing a weakening of the field withinthe zones of the billet in front of the said auxiliary poles.

The invention will be described reference being made to the drawingwhich shows a cross-field furnace through which the articles are fedhorizontally. 'T he right-hand half of the figure is a section throughthe furnace and the left-hand half is a view of the same.

The furnace consists of two laminated yokes ll carrying the main polesZaand 211 from which the alternating field emerges, and of two auxiliarypoles 3 turned 90 with respect to the main poles. The winding is dividedvertically into two equal parts 4a and 4b each embracing a main pole andhaving the same current direction on the one yoke and opposite directionon the other yoke. These winding parts arranged at an angle of 45 withrespect to the main and auxiliary poles are separated from each "iceother by the auxiliary poles 3 having no windings. The billet isdesignated by 5. In analogy with what is the case in direct currentcommutator machines an auxiliary pole without winding weakens the branchof the main field within the billet below the arc of the auxiliary polein an amount inversely proportional to the width of the air gap betweenthe auxiliary pole and the billet. The field diagram is shown for aquadrant of the furnace and a billet having square cross-section androunded-off edges. Obviously such a billet has to be positioned with itsone diagonal in the direction of the axis of the main poles. he fielddiagram shows both that it is easy to find a place within the main pole2b for the supporting elements of the conveyor chain, not shown, andthat the field intensity within the loss zone of the billet i. e. thepenetration depth indicated by the measure '7 will be largest at theauxiliary pole, despite of its considerable width as shown in thedrawing by way of example. If the air gap of the auxiliary pole had beendecreased additionally, it had been possible to further weaken there thefield somewhat, but the power distribution obtained has been deemed tobe sufficiently uniform. To this advantageous result contributes thefact that according to another feature of the invention the currentdensity of the magnet coils decreases in the direction from the mainpoles toward the auxiliary poles.

This is indicated on the right-hand side of the drawing in that sixconductors are shown having heights increasing in the said direction.The arrangement is usable for cylindrical billets having circular orelliptical cross-section. The air gap in the upper main pole is providedfor the sake of symmetry. It may be bridged by a yoke piece. The windingis protected against heat radiation from the billet by wedges 8 ofrefractory material, and against over-temperatures by cooling loops 9embedded within the auxiliary poles.

I claim as my invention:

1. A cross-field furnace for induction heating of metal lic articleswithin an alternating field extended planeparallelly and at right anglesto the longitudinal axis of the article, and symmetrically to thehorizontal as well as to the vertical planes through this axis, andwhich held is completed through the article and through laminated yokes,said yokes having extended inwardly four distinct poles, two poles ofwhich being arranged coaxially with different polarities and working asmain poles provided with windings, while the other two poles Working asauxiliary poles for weakening the field within the Zones of the articlefacing the auxiliary poles are arranged at an angle of with respect tothe said main poles and have no windings.

2. A cross-field furance according to claim 1, wherein the windings ofthe main poles are arranged so that their axial coil surfaces form 45angles with the symmetry planes of the main and auxiliary poles.

3. A cross-field furnace according to claim 2, wherein the currentdensity of the windings is decreased from the main poles towards theauxiliary poles for reducing the surface field intensity of the articlein the same direction.

4. A cross-field furnace according to claim 1, wherein the windings ofthe main poles are so arranged that their axial coil surfaces form 45angles with the symmetry planes of the main and auxiliary poles, and oneof the said main poles is provided with a gap for the passage of aconvcyer means.

References Cited in the file of this patent UNITED STATES PATENTS2,176,488 Dreyfus Oct. 17, 1939 2,480,315 Bennett Aug. 30, 19492,667,524 Dreyfus et al. Jan. 26, 1954

